Semiconductor device with buried inverse T-type field region

ABSTRACT

The present invention relates to a semiconductor and a method for fabrication thereof and particularly to a semiconductor having a field oxide having a shape such that the lower part is wider that the upper part. 
     Therefore, according to the present invention, the ion implantation process for forming a channel stop region becomes unnecessary, because of the effect of accurate insulation between the devices and the pn junction area can be decreased, so that the junction capacitance becomes decreased. Furthermore, because LOCOS edge does not coincide with the junction edge, the leakage current due to the damage of the edge is not generated. Because a field oxide is of the buried inverse T-type, the effective width of the device is increased more than that of a mask. Because the bird&#39;s beak is not generated, the problem due to the narrow width can be settled.

This application is a continuation of U.S. Application Ser. No.07/974,978, filed Nov. 12, 1992, now abandoned, which is a division ofU.S. application Ser. No. 07/856,020, filed Mar. 23, 1992, and nowissued as U.S. Pat. No. 5,182,226.

BACKGROUND OF THE INVENTION

The present invention relates to a semiconductor device and a method forfabrication thereof having a field oxide of the buried inverse T-typesuited to sub-micron MOS devices.

FIG. 1 shows a cross-sectional view of a semiconductor device where afield oxide is formed using a conventional LOCOS process (LocalOxidation of Silicon).

In the prior art, when MOS devices are fabricated, the field oxide isformed using the conventional LOCOS to isolate devices.

Thus, as shown in FIG. 1, a field oxide layer 2 is grown on a fieldregion of a Si substrate 1 using a nitride layer (not shown herein) anda gate 3 is formed at a predetermined region, and then predeterminedimpurities are implanted on both sides of gate 3 to form the source anddrain regions 4.

Furthermore, because, when the field oxide 2 is grown, it penetratesonly a little within Si substrate 1, predetermined impurities areimplanted in a field region to form a channel stop for insulationtransistors.

However, the conventional fabrication process for forming the fieldoxide has disadvantages in that the effective area of the device isdecreased, because of the generation of the bird beak and thecapacitance is increased due to the pn junction. Furthermore, leakagecurrent is generated by the damage of the edge portion, so that it isnot able to completely insulate the device.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a semiconductordevice having a field oxide of the buried inverse T-type.

It is another object of the present invention to provide a method forfabrication of the semiconductor device for forming a field oxide of theburied inverse T-type using oxygen or nitrogen ion implantation.

To achieve this object of the present invention, there is provided asemiconductor device isolated by a field oxide in the shape of a buriedinverse T, in which the lower part is wider than the upper part.

And, there is provided a method for fabrication of the semiconductordevice, which comprises the steps of:

successively depositing a pad nitride film, a first nitride film and afirst oxide film on a Si substrate;

exposing the Si substrate of field region and forming the side wall of asecond nitride film;

implanting ion impurities into the exposed substrate to a predetermineddepth;

removing the first oxide film and second nitride film and successivelydepositing a second oxide film and a second nitride film on the wholesurface;

etching the third nitride film to expose the fixed portion of the Sisubstrate;

implanting the impurities with lower energy than the first ionimplantation;

forming a field oxide by heat treatment of the impurities implantedwithin the substrate;

removing the remaining third nitride film, second nitride film, firstnitride film and pad nitride film; and

forming a transistor in an active region isolated by the field oxide.

BRIEF DESCRIPTION OF THE INVENTION

The features and advantages of the present invention will be moreclearly appreciated from the following description of the preferredembodiments of the invention taken in conjunction with the accompanyingdrawings in which:

FIG. 1 is a cross-sectional view of a semiconductor device in which afield oxide is formed using the conventional LOCOS.

FIGS. 2A through 2E are cross-sectional views illustrating the deviceafter various operations in a fabrication process forming a field oxideof the buried inverse T-type according to a preferred embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

A semiconductor device and a method for fabrication thereof according tothe present invention will be described in more detail with reference tothe various views in accompanying FIG. 2.

FIGS. 2A through 2E are cross-sectional views of the device aftercompletion of various steps in a fabrication process for manufacturing asemiconductor device having the buried inverse T-type according to apreferred embodiment of the present invention.

A pad nitride film 12, a first nitride film 13 and a first oxide film 14are successively deposited on a Si substrate 11. The Si substrate 11 ofthe field region is exposed by using an active mask (not shown herein).

Then, the second nitride film is thinly deposited and then etched by anRIE process to form the side wall 15.

The fixed impurities, such as the oxygen ions or the nitrogen ions, arethen implanted into the exposed Si substrate 11 to a predetermineddepth.

Herein, the first ion implantation condition is that the impuritiesshould be implanted into the surface of the Si substrate 11 to a depthof about 0.5 μm with an energy of from about 150 to 250 KeV.

Furthermore, amount of the dose is on the order of from 10¹⁷ /cm² to20¹⁹ /cm².

Henceforth, as shown in FIG. 2B, the first oxide film 14 and the sidewall 15 are removed and the second oxide film 16 and the third nitridefilm 17 are successively deposited on the whole surface.

Then, as shown in FIG. 2C, the third nitride film 17 is etched by RIE toform the side wall 17a, and the oxygen ions or the nitrogen ions areimplanted with lower energy against the Si substrate 11.

Herein, the second ion implantation condition is that the impuritiesshould be implanted from the surface of the Si substrate 11 to a depthof about 0.5 μm with energy of from about 50 to 100 KeV.

Furthermore, the amount of the dose is on the order of from 10¹⁷ /cm² to10¹⁹ /cm².

Henceforth, as shown in FIG. 2D, a heat treatment process of about 800°to 950° is performed at the oxygen ion implanted region to form a fieldoxide 18.

Then the side wall, the second oxide film 16, the first nitride film 13and the pad nitride film 12 are removed. Accordingly, the field oxide 18of the buried inverse T-type is formed.

Henceforth, as shown in FIG. 2E, the gate 19 and the source and drainregion 20 are formed in the active region of the isolated field oxide 18of the buried inverse T-type according to the present invention.

According to the present invention use, the ion implantation process forforming a channel stop region becomes unnecessary, because of the effectof accurate insulation between the devices and the pn junction area canbe decreased, so that the junction capacitance becomes decreased.

Furthermore, because the LOCOS edge does not coincide with the junctionedge, the leakage current due to the damage of the edge is notgenerated. Because the field oxide is of the buried inverse T-type, theeffective width of the device is increased more than that of a mask.Because the bird's beak is not generated, the problem due to the narrowwidth can be settled. It will be understood by those skilled in the artthat the foregoing description is in terms of a preferred embodiment ofthe present invention, wherein various changes and modifications may bemade without departing from the spirit and scope of the invention, asset forth in the appended claims.

What is claimed is:
 1. A semiconductor device having a nitride fieldregion of the buried inverse T-type comprising:a semiconductorsubstrate; at least one gate electrode having opposite edges formed onthe semiconductor substrate; source and drain regions formed below theopposite edges, respectively, of each gate electrode; nitride fieldregions formed adjacent the source and drain regions, wherein a lowerpart of each field region contacts a lower part of the adjacent one ofthe source and drain regions, and an upper part of each field regioncontacts a side of the adjacent one of the source and drain regions,such that the lower part of each field region is wider than the upperpart of the field region.
 2. A semiconductor device having a nitridefield region of the buried inverse T-type comprising:a semiconductorsubstrate; at least one gate electrode having opposite edges formed onthe semiconductor substrate; drain and source regions formed below theopposite edges, respectively, of each gate electrode; nitride lowerfield regions formed adjacent the source and drain regions, wherein eachlower field region extends below and contacts a lower part of theadjacent one of the source and drain region; and nitride upper fieldregions formed adjacent the source and drain regions and above the lowerfield regions, wherein each upper field region contacts a side part ofthe adjacent one of the source and drain region.